extract UDP fast path type checking to peek_packet_type

Author: ari-kl

libqretprop/DeviceControllers/deviceTools.py

@@ -21,6 +21,7 @@
     StreamStartPacket,
     decode_packet_server,
     get_packet_len,
+    peek_packet_type,
 )
 
 
@@ -215,7 +216,7 @@ async def udpListener() -> None:
                     if isinstance(device, SensorMonitor):
                         # Fast-path for DATA packets (100% of UDP traffic):
                         # Check packet type from raw bytes without full decode_packet.
-                        packet_type = data[1] # Important: this relies on header structure outside of decode_packet
+                        packet_type = peek_packet_type(data)
                         if packet_type == PacketType.DATA:
                             # Only decode if already verified as DATA packet
                             packet = decode_packet_server(data)

libqretprop/protocol.py

@@ -53,6 +53,19 @@ def get_packet_len(data: bytes) -> int:
     _check(_lib.qlcp_get_packet_len(data_len, buf, len(data)), "get_packet_len")
     return int(data_len[0])
 
+
+def peek_packet_type(data: bytes) -> int:
+    """Peek the packet-type byte from a raw packet header.
+
+    Accesses the packet type from raw bytes for fast-path packet type checks without a full decode
+
+    Raises `QLCPError` if the provided buffer is too short to contain that byte.
+    """
+    if len(data) < 2:
+        raise QLCPError(f"packet too small to peek type: {len(data)} bytes")
+    # In QLCP v2 the packet-type is the second byte of the header
+    return data[1]
+
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 # ENUMS
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